Marin County, CA Environmental Rules: Vehicle Idling Restrictions (2026)

040 sets 'Outdoor Construction Activities' standards that apply on top of any Federal, State, or local permit conditions for outdoor work needing a Building Permit. Subsection C, 'Dust and Emission Control,' applies specifically to projects involving ground disturbance that are subject to environmental review, and item 6 requires idling times to be minimized either by shutting equipment off when not in use or by capping idling at five minutes, citing the California Airborne Toxics Control Measure at Title 13, Section 2485 of the California Code of Regulations.

The same subsection pairs the idling limit with other dust-control measures: watering exposed unpaved surfaces twice daily, covering haul trucks, sweeping mud or dirt track-out with wet power vacuum sweepers at least once a day (dry sweeping is banned outright), capping unpaved-road vehicle speeds at 15 miles per hour, paving roadways and driveways as soon as possible, and having a certified emissions evaluator check that equipment is properly tuned. Clear signage stating the idling limit must be posted at every construction access point so crews see it before they enter the site.

Because the rule is keyed to environmental review rather than every Building Permit, a small remodel that doesn't trigger CEQA review typically won't carry this specific condition, though the Director can still impose it on a case-by-case basis.